The most common method for softening water is the cation exchange method in which hard water is brought into contact with beads of a cation exchange resin whereby sodium ions in the resin are replaced by the calcium and magnesium ions that were in the water and the sodium ions are taken up by the water. When the resin is essentially depleted of sodium ions it is recharged by passing brine through the bed of resin beads to remove the calcium and magnesium ions as the soluble chlorides and replace them with the sodium ions. To generate the brine, sodium chloride in the form of pellets or blocks is placed in a tank and is dissolved by allowing it to sit in a measured amount of water in the tank for a sufficient time before each recharging cycle.
In the production of salt blocks, a release agent is required to minimize wear and damage to the inner surfaces of the block press mold box. These surfaces are commonly those of a stainless steel liner of the box. Calcium stearate is believed to be the most commonly used salt block release agent in the salt industry. The residue of calcium stearate on the surface of such blocks is insoluble when the salt is dissolved in a brine tank, however, and the accumulation of said residue forms an unsightly surface scum in the tank. In U.S. Pat. No. 5,478,515, which issued from application Ser. No. 08/055,127, which is a grandparent to this application, a powdered water-soluble release agent is sprayed onto the molding surfaces of the block press mold box. Some of the powder is transferred to the blocks but its presence does not generate an unsightly scum in brine tanks used in water softening systems.
Briquetting is a method for compacting salt which comprises introducing crystalline salt into the nip zone of a pair of intagliated, counter-rotating rolls in register with one another in a briquetting press the press, compacting the salt between the rolls into pellets with pressure, and discharging the pellets as the roll faces separate from one another. Because of the scum problem, the use of a release agent has not been seen to be much of an advantage in the formation of salt pellets on a roll-press. Now, the use of a water-soluble release agent has solved that problem.
This invention relates to a method for molding a water soluble salt with the aid of a water soluble release agent which facilitates the release of the compacted salt from the mold. More particularly, this invention relates to an improved method for compacting fine crystals of a water soluble salt in a block press mold box or a roll-type briquetting press whereby the wear of the bearings and other components of each is minimized. Still more particularly, the invention relates to a method for compacting fine crystals of the salt using a release agent whose presence on the blocks or pellets does not generate an unsightly scum in brine tanks used in water softening systems. Both blocks and pellets must resist handling and shipping damage and disintegration when stored in brine.
The term mold is defined for the purposes of this invention to include both a block press mold box and a roll-type briquetting press. The term salt is defined for the purposes of this invention to mean all water-soluble halides of sodium and potassium. The term salt compact is defined for the purposes of this invention to mean all compacted forms of salt, as exemplified by blocks, salt licks, bricks, pellets, nuggets, cubes, flakes, briquettes, and pillows. The special term salt block, however, is defined to mean a compressed mass of sodium chloride and additives which is commonly made in two sizes--25 and 50 pounds. The approximate dimensions of the 50 pound block are 8".times.8".times.11". Bricks are about 6".times.4".times.2". Salt pellets are generally rounded bodies having a volume of about 0.1 to about 0.2 cubic inch. Flat flakes weighing from 2 to 20 grams are made by compressing salt between smooth rolls and breaking up the sheet thus formed.